1. Field of the Invention
The present invention is directed to wireless telecommunications and, more particularly, to a method and system for processing calls and providing local number portability in a wireless communications environment.
2. Background
Local number portability ("LNP") allows telephone subscribers to keep their phone numbers when they change residences and/or service providers. A mandate of the Telecommunications Act of 1996, this option must have been made available to wireline subscribers in the top 100 markets by the end of 1998. The advantages of retaining one's phone number were recognized in exchange tariffs as early as the 1960s. The issue also cropped up in the 1980s and early 1990s, when portability for 800 numbers was instituted to encourage competition in the toll-free long-distance sector. More recently, a survey conducted by the Gallup poll found that nearly 80 percent of residential subscribers and 90 percent of business subscribers would be unwilling to change service providers if they had to surrender current phone numbers.
While implemented in land-based telephone networks, LNP provides additional challenges when implemented in wireless networks. In land-based networks, queries are launched to a number portability database ("NPDB") containing a list of telephone numbers that have switched (or "ported") to other service providers. The NPDB includes the number and routing information of the new service provider (the "ported-to service provider") and returns this information (the "Local Routing Number") to a switch in the network of the original service provider (the "donor service provider"). The switch can then route the call to the proper network.
In a wireless network, local number portability is more complicated. One initial difference is that many wireless networks identify the subscriber's mobile set with a Mobile Identification Number ("MIN") which is used in part to complete the call. A home location register ("HLR") stores the unique MIN and Electronic Serial Number ("ESN") contained in each subscriber's mobile set and associates this with the mobile directory number ("MDN"). Currently, the MIN and MDN values are the same number. With LNP, these values are likely to be different for ported numbers.
Each time a call is made to a wireless subscriber, the wireless service provider uses the MDN to check the HLR to determine the location of the mobile subscriber. In order for the call to reach the correct wireless service provider, the NPDB may be accessed. Thus, the data contained in each HLR must be synchronized with the information in the NPDB in order for the call to ultimately reach the subscriber. The synchronization of HLRs and NPDBs between the old and new service provider is a large challenge facing wireless number portability. Synchronization of the NPDBs is accomplished in part with the services of the Number Portability Administration Center ("NPAC") which serves as a "master coordinator" of the NPDB information among service providers. However, each service provider must coordinate their HLRs and NPDBs by themselves. If done incorrectly, calls may not complete to the subscriber.
LNP also impacts current procedures in which service providers populate HLRs with blocks of new numbers and process vacant numbers. Typically, when a new central office codes (i.e., the NPA-NXX portion of the directory number) is obtained, it is provisioned on the serving mobile switching center ("MSC") so that calls to that number result in a query to the HLR. Each code served by the MSC allows the service provider to serve up to 10,000 individual numbers. Initially, the numbers are not assigned to subscribers ("vacant") but as time goes on they are assigned to new subscribers and considered "active". Calls to vacant numbers are routed to an announcement indicating the number is not in service. Rather than initially listing all 10,000 numbers with a indicator as "active" or "vacant", the HLR only lists active numbers. It is presumed that an absent number is a vacant number.
When a service provider ports in a subscriber, the central office code must be listed as one that is served by the MSC. Thus, the central office code for that number is provisioned on the MSC. In addition, the subscriber's number is populated in the HLR. Thus, the HLR lists that number as active. Since the other numbers in the code are not in the HLR, the HLR treats them as vacant. However, those other numbers are not necessarily vacant and are actually allocated to other service providers--either the original service provider assigned the code or to some other ported-to service provider.
Thus, numbers not listed in the HLR for which the NPA-NXX is provisioned in the MSC can represent three situations: (1) the subscriber canceled his service; (2) the subscriber ported out to another service provider; or (3) that number was never served by the MSC but is allocated to some other provider. These situations must be distinguished. Where a subscriber has canceled service, the service provider should provide an announcement to a caller that the number is no longer in service or has been disconnected. Where a customer has ported out his number or the number is allocated to some other service provider, the MSC should route the call to the correct service provider. Currently, when a query is launched to the HLR and it does not find a number present, it presumes it is vacant. The current procedures between the MSC and HLR cannot distinguish between a vacant number, ported out number, or number assigned to another service provider.
Unfortunately, providing HLRs with the proper functionality would be inordinately expensive and time-consuming. It would require all 10,000 numbers in each number in a central office code to be explicitly identified. In addition, the signaling protocol between the MSC and HLR would have to be modified to communicate this new status information. Furthermore, significant impact to a service provider's provisioning systems and business flows would be required to support this. A method that allows properly distinguishes the situation without modification of the HLR would facilitate the introduction of wireless number portability.